Electrostatically controlled magnetic logic device

ABSTRACT

A magnetic logic cell includes a first electrode portion, a magnetic portion arranged on the first electrode, the magnetic portion including an anti-ferromagnetic material or a ferrimagnetic material, a dielectric portion arranged on the magnetic portion, and a second electrode portion arranged on the dielectric portion.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under contract numberN66001-11-14110 awarded by Defense Advanced Research Projects Agency.The government may have certain rights in the invention.

FIELD OF INVENTION

The present invention relates generally to method and devices involvingmagnetic logic devices, and more specifically, to methods and devicesinvolving electrostatically controlled magnetic logic devices.

DESCRIPTION OF RELATED ART

FIG. 1 illustrates a side view of a prior art example of anelectrostatically controlled cell (cell) 100 in a first state. In theillustrated example, the cell 100 includes a first electrode 102connected to ground. A ferromagnet portion 104 is arranged on the firstelectrode 104. A dielectric portion 106 is arranged on the ferromagnetportion 104, and a second electrode 108 is arranged on the dielectricportion 106. A ferromagnetic layer has all magnetic atomic momentspointing in the same direction (and may include an alloy of 2 differentcompounds such as, for example CoFe). A ferrimagnetic layer has somemoments pointing in one direction and some moments pointing in theopposite direction, for instance in the TbFe alloy, even though most ofthe alloy is amorphous and Fe and Tb sites have random spatiallocations, all of the Tb atoms form a magnetic sublattice (the Tb atomsare ferromagnetically coupled to each-other) and have their momentspointing in one direction, and all of the Fe atoms form another magneticsublattice and have their magnetic moments pointing towards the oppositedirection. The magnetic moments of individual Tb and Fe atoms aredifferent therefore even though the magnetic sublattices formed by Tband Fe are oriented towards opposite directions they do not necessarilycancel-out each other so a macroscopic moment is possible.

The ferromagnetic portion 104 is shown with a number of arrowsindicating the direction of the magnetic moment of the atoms arranged inthe ferromagnetic portion 104. When a voltage (V1) is applied to thesecond electrode 108, the arrows are shown orientated in a firstdirection. The application of the voltage V1 to the second electrodeaffects a junction region 101 of the ferrimagnet portion 104 that isoperative to impart a change in the electromagnetic energy in thesystem. This change results in the orientation of the atomic magneticmoment spins of the atoms in the ferromagnetic portion 104 as shown.

FIG. 2 illustrates the prior art example of the cell 100 in a secondstate. Referring to FIG. 2, a second voltage (V2) is applied to thesecond electrode 108. The application of the V2 voltage affects thejunction region 101 of the ferromagnetic portion 104 that changes theorientation of the magnetic moment of the atomic sites in theferromagnetic portion 104. In FIG. 1 the magnetic orientation is “inplane” while in FIG. 2 the magnetic orientation of the ferromagneticportion 104 is “out of plane.” GIvne the two states, the cell 100 can beused as a magnetic logic device.

BRIEF SUMMARY

According to an embodiment of the present invention, a magnetic logiccell includes a first electrode portion, a magnetic portion arranged onthe first electrode, the magnetic portion including ananti-ferromagnetic material or a ferrimagnetic material, a dielectricportion arranged on the magnetic portion, and a second electrode portionarranged on the dielectric portion.

According to another embodiment of the present invention, a magneticlogic cell includes a first electrode portion, a magnetic portionarranged on the first electrode, the magnetic portion including a firstlayer of anti-ferromagnetic material or ferrimagnetic material, adielectric portion arranged on the magnetic portion, and a secondelectrode portion arranged on the dielectric portion.

According to yet another embodiment of the present invention, a magneticlogic cell includes a first electrode portion, a magnetic portionarranged on the first electrode, the magnetic portion including a firstlayer of anti-ferromagnetic or ferrimagnetic material disposed on thefirst electrode, a dielectric portion arranged on the magnetic portion,and a second electrode portion arranged on the dielectric portion.

According to another embodiment of the present invention, a method forfabricating a magnetic logic cell includes depositing and patterning alayer of conductive material on a substrate to define a first electrode,depositing a first layer of anti-ferromagnetic or ferrimagnetic materialdisposed on the first electrode, depositing a dielectric material layerover the first layer of magnetic material, patterning the first layer ofmagnetic material, and the dielectric material layer to define amagnetic portion and a dielectric portion of the cell, and forming asecond electrode portion in contact with the dielectric material layer.

According to another embodiment of the present invention, a method forfabricating a magnetic logic cell includes depositing and patterning alayer of conductive material on a substrate to define a first electrode,depositing a dielectric material layer over the first electrode,depositing a first layer of anti-ferromagnetic or ferrimagnetic materialon the dielectric material layer, patterning the first layer of magneticmaterial, and the dielectric material layer to define a magnetic portionand a dielectric portion of the cell, and forming a second electrodeportion in contact with the first layer of ferrimagnetic material.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a side view of a prior art example of anelectrostatically controlled logic cell (cell) in a first state.

FIG. 2 illustrates a side view of the prior art example of the cell ofFIG. 1 in a second state.

FIG. 3 illustrates an exemplary embodiment of a logic cell in a firststate.

FIG. 4 illustrates the exemplary embodiment of the logic cell of FIG. 3in a second state.

FIG. 5 illustrates another exemplary embodiment of the ferrimagneticportion.

FIG. 6 illustrates another exemplary embodiment of the ferrimagneticportion.

FIG. 7 illustrates another exemplary embodiment of the ferrimagneticportion.

FIG. 8 illustrates another exemplary embodiment of the ferrimagneticportion.

DETAILED DESCRIPTION

Computational schemes based on the switching of magnetic moment(spintronics) used in magnetic logic cells may be controlled using lowervoltages than the voltages used in complementary metal oxidesemiconductor (CMOS) based memory/logic devices. The voltage control ofsome devices may be less than one volt, which facilitates the use ofhigher clock speeds in processors. The use of devices based onferromagnetic materials provides a low voltage control solution, howeverprevious ferromagnetic devices have exhibited a relatively slow stateswitching speed (e.g., 0.5 nanoseconds). The low switching speeds areundesirable. The exemplary embodiments described below provide a devicehaving a relatively fast switching speed with out-of-plane to in-planereversal as fast or potentially faster than 10 ps. The exemplaryembodiments include logic cells that include layers of antiferromagnetsand ferrimagnets that affect a low-energy and fast voltage inducedcontrol using anisotropy control and magnetization switching

FIG. 3 illustrates an exemplary embodiment of a logic cell (cell) 300 ina first state. The cell 300 includes a first conductive electrodeportion 302 that is connected to ground. A ferrimagnetic (orantiferromagnetic) portion 304 is arranged in contact with the firstconductive electrode portion 302. A non-conductive dielectric portion306 is arranged on the ferrimagnetic (or antiferromagnetic) portion 304.The dielectric portion 306 may include any suitable dielectric materialsuch as, for example, MgO, HfO₂, Al₂O₃, TiO₂ more generally all High-kdielectrics (such as ZrO2, La2O3, TiO2, SrTiO₃, BaSrTiO₃, PbLaTiO₃). Asecond conductive electrode portion 308 is arranged on the dielectricportion 306. The cell 300 may be arranged on a substrate (not shown) andmay be arranged in an array with any number of cells 300.

The first and second conductive electrode portions 302 and 308 mayinclude any suitable conductive material such as, for example, Al, Au,Ag, Pt, Pd, Ti, Ta, Ru or Cu and so on. The ferrimagnetic (orantiferromagnetic) portion 304 is illustrated with arrows that indicatethe direction of the magnetic moment of the atoms that are arranged inthe ferrimagnetic (or antiferromagnetic) portion 304. In the illustratedembodiment, a first voltage V1 is applied to the second conductiveelectrode portion 308 such that the magnetic orientation of theferrimagnetic (or antiferromagnetic) portion 304 is shown “in plane”however, the orientation of the spins are in opposing directions. Inthis regard, the sum of the vectors representing the orientation of themagnetic moments is approximately zero or close to zero. Theferrimagnetic (or antiferromagnetic) portion 304 may include, forexample, an alloy material such as, for example Tb_(1-x)Fe_(x),Gd_(1-x)Fe_(x), Dy_(1-x)Fe_(x),Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co_(y), Dy_(1-x-y)Fe_(x)Co_(y)more generally materials containing rare earth metals and magnetictransition metals elements, in which the magnetic sublattice of rareearth ions and the one formed by the Transition metal ions areantiferromagnetically coupled so that the moment of the two sublatticesare pointing towards opposite directions. Moment compensation is reachedwhen the two sublattices have equal but opposite moments.

FIG. 4 illustrates the cell 300 in a second state where a second voltageV2 is applied to the second conductive electrode 308. The application ofthe V2 voltage results in a change in state of the ferrimagnetic (orantiferromagnetic) portion 304 such that the orientation of the spins ofthe atoms is “out of plane” however, the directions of the magneticmoments of the atoms are in opposing directions. The cell 300 may befabricated by, depositing a layer of conductive metallic material suchas, for example, Al, Au, Ag, Pt, Pd, Ti,Ta, Ru or Cu on a substrate.Portions of the layer of conductive metallic material may be removed by,for example, a lithographic patterning and etching process. A layer offerrimagnetic material such as, for example Tb_(1-x)Fe_(x),Gd_(1-x)Fe_(x), Dy_(1-x)Fe_(x), Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co_(y), Dy_(1-x-y)Fe_(x)Co_(y). The layers can befabricated by using, for example, a magnetron sputtering technique byeither deposition directly from a single phase sputtering source such asTb_(1-x)Fe_(x) or cosputtering using two or more sources namely one forthe rare earth metal such as for instance Tb and one or two for thetransition metal such as Fe. A dielectric layer is disposed on the layerof ferrimagnetic material, which may include any suitable dielectricmaterial such as, for example, MgO, HfO₂, Al₂O₃, TiO₂ more generally allHigh-k dielectrics (such as ZrO2, La2O3, TiO2, SrTiO₃, BaSrTiO₃,PbLaTiO₃). A second layer of conductive metallic material is disposed onthe dielectric layer. A suitable lithographic etching process may beperformed to pattern the cell 300 as illustrated in FIG. 3.

FIG. 5 illustrates an alternate exemplary embodiment of theferrimagnetic (or antiferromagnetic) portion 304 in the first state asshown in FIG. 3. It shall be understood that portion 304 may also beconsidered an “artificial ferrimagnet” as it may be composed offerromagnetic layers each at least several atoms thick In this regard,the ferrimagnetic (or antiferromagnetic) portion 304 is formed fromlayers 502 and 504 of alternating materials having thicknesses of theorder of 2-20 Å, for example Tb 20 Å/Fe 20 Å . . . The layer 502includes a ferromagnetic material such as, for example, Tb, Dy, or Gd,Nd, Sm more generally all of the rare earth metals. The layer 504disposed on the layer 502 includes a ferromagnetic material such as, forexample, Fe, Co, Ni, Co_(x)Fe_(1-x), Co_(1-x-y)Fe_(x)B_(y). Therespective magnetic properties of the layers 502 and 504 and therelative [antiferromagnetic] arrangement of the layers 502 and 504results in a ferrimagnetic (or antiferromagnetic) portion 304 that has amagnetic moment that is substantially neutral or substantially close tozero (e.g., 0-20 electro magnetic units (EMU) per cubic centimeter;i.e., at or close to the magnetization compensation point). Though thelayer 504 is shown in contact with the dielectric portion 306 in theillustrated embodiment, in an alternate embodiment, a layer 502 may bein contact with the dielectric portion 306. In some embodiments, anultra thin metal layer may be inserted or “dusted” in the interfacebetween the dielectric portion 306 and the ferrimagnetic (orantiferromagnetic) portion 304. (e.g, with a thickness of the order of amonolayer or 2-3 Å) in order to enhance the contribution to the surfacemagnetic anisotropy of layer 304, for instance metallic layer such as Ptor Pd or Bi or more generally metals with a high atomic number hencewith a high spin orbit coupling.

FIG. 6 illustrates the ferrimagnetic (or antiferromagnetic) portion 304as described in FIG. 5 when the cell 300 in in the second state. In thisregard, the layers 502 and 504 have atoms with magnetic moments that areperpendicular to the plane of the film, however the magnetic moments areorientated in opposing directions.

FIG. 7 illustrates an alternate exemplary embodiment of theferrimagnetic (or antiferromagnetic) portion 304 in the first state asshown in FIG. 3. In this regard, the ferrimagnetic (orantiferromagnetic) portion 304 is formed from layers 502 and 504 asdescribed above in FIG. 5, however the layer 504 that includes aferromagnetic material such as a transition metal, like Fe, Co, or Ni,is disposed on the second electrode portion 302 (of FIG. 3), and thelayer 502 that includes a second ferromagnetic material such as forinstance a rare earth ferromagnet, like Tb or Gd, is disposed on thelayer 504, the thicknesses are chosen so that 502 and 504 are coupledantiferromagnetically. Any number of alternating pairs of layers 504 and502 may be included in the ferrimagnetic (or antiferromagnetic) portion304.

FIG. 8 illustrates the ferrimagnetic (or antiferromagnetic) portion 304as described in FIG. 7 when the cell 300 in in the second state. In thisregard, the layers 502 and 504 have atoms with magnetic moments that areout of plane, however the magnetic moments are orientated in opposingdirections.

The combination of the transition metal and the rare earth in theferrimagnetic (or antiferromagnetic) portion 304 result in a small (zeroor near zero) moment. Thus, at a given applied voltage, theferrimagnetic (or antiferromagnetic) portion 304 undergoes a highereffective field (electric and magnetic) as compared to devices havingferromagnets. Each sublattice is subjected to the exchange field(orientated in an opposing direction to an adjacent sublattice) of theadjacent sublattice. The additional field appears to increase thedamping rate and provides for faster magnetization dynamics. The effectprovides very fast reversal of the magnetization of the MRAM device 300with voltage-induced anisotropy modulation at the interface 301 of thedielectric portion 306 and the ferrimagnetic (or antiferromagnetic)portion 304.

The application of the voltage to the top electrode 108 induces anelectric field across the dielectric in region 106 and results in achange in the carrier concentration of the interfacial region 101thereby changing the contribution of this region to the overall magneticanisotropy of the magnetic film 104. This results in a rotation of themagnetic moments on each atomic site of the region 104. The anisotropyaxis defines the energetically favorable direction for the magneticmoments of a given material when no magnetic field is applied to portion304 and interfacial anisotropies form region 301. (This includes thecontribution from the bulk and the surface/interface, or portion 301, ofthe given material with the dielectric portion 306, the magnetic momentdirection is the sum or total contributions of both bulk anisotropiesfrom portion 304 and surface anisotropies from portion 301, the latterinterfacial contribution may be modulated with the electric field, hencethe magnetic moment of portion 304 and 301 can be rotated when thesurface anisotropy represents more than 50% of the total anisotropy(bulk+interface) which is the case only of very thin magnetic layers ofless than 20 Å).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. A magnetic logic cell comprising: a first electrode portion; ananti-ferromagnetic material or ferrimagnetic material arranged directlyon the first electrode; a dielectric portion arranged on the magneticportion; and a second electrode portion arranged on the dielectricportion.
 2. The cell of claim 1, wherein the magnetic portion has a netmagnetic moment of approximately a compensation point of the magneticportion.
 3. The cell of claim 1, wherein the magnetic portion isarranged in contact with the first electrode portion.
 4. The cell ofclaim 1, wherein the first electrode portion and the second electrodeportion include a conductive material.
 5. The cell of claim 1, whereinthe magnetic orientation of the magnetic portion is operative to changestates when a voltage is applied to the first electrode portion.
 6. Thecell of claim 1, wherein the ferrimagnetic material includesTb_(1-x)Fe_(x), Gd_(1-x)Fe_(x), Dy_(1-x)Fe_(x),Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co, or Dy_(1-x-y)Fe_(x)Co.
 7. Thecell of claim 1, wherein the ferrimagnetic material includes a magneticsublattice of rare earth ions and the sublattice formed by transitionmetal ions that antiferromagnetically coupled so that moments of thesublattices point towards opposite directions.
 8. A magnetic logic cellcomprising: a first electrode portion; a first layer of ananti-ferromagnetic material or a ferrimagnetic material arrangeddirectly on the first electrode; a dielectric portion arranged on themagnetic portion; and a second electrode portion arranged on thedielectric portion.
 9. The cell of claim 8, wherein the first layer is afirst layer of ferrimagnetic material and the magnetic portion furthercomprises: a layer of anti-ferromagnetic material arranged on the firstlayer of ferrimagnetic material; and a second layer of ferrimagneticmaterial arranged on the layer of anti-ferromagnetic material.
 10. Thecell of claim 8, wherein the magnetic portion has a net magnetic momentof approximately a compensation point of the magnetic portion.
 11. Thecell of claim 8, wherein the layer of anti-ferromagnetic material isarranged in contact with the first electrode portion.
 12. The cell ofclaim 8, wherein the first electrode portion and the second electrodeportion include a conductive material.
 13. The cell of claim 8, whereinthe magnetic orientation of the magnetic portion is operative to changestates when a voltage is applied to the first electrode portion.
 14. Thecell of claim 8, wherein the ferrimagnetic material includesTb_(1-x)Fe_(x), Gd_(1-x)Fe_(x), Dy_(1-x)Fe_(x),Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co, or Dy_(1-x-y)Fe_(x)Co.
 15. Thecell of claim 8, wherein the ferrimagnetic material includes a magneticsublattice of rare earth ions and a sublattice formed by transitionmetal ions that antiferromagnetically coupled so that moments of thesublattices point towards opposite directions.
 16. A magnetic logic cellcomprising: a first electrode portion; a first layer of ananti-ferromagnetic or a ferrimagnetic material disposed directly on thefirst electrode, the magnetic portion including a first layer of ananti-ferromagnetic or a ferrimagnetic material disposed on the firstelectrode; a dielectric portion arranged on the magnetic portion; and asecond electrode portion arranged on the dielectric portion.
 17. Thecell of claim 16, wherein the first layer is a first layer offerrimagnetic material and the magnetic portion further comprises: alayer of anti-ferromagnetic material arranged on the first layer offerrimagnetic material; and a second layer of ferrimagnetic materialarranged on the layer of anti-ferromagnetic material.
 18. The cell ofclaim 16, wherein the magnetic portion has a net magnetic moment ofapproximately a compensation point of the magnetic portion.
 19. The cellof claim 16, wherein the ferrimagnetic material includes Tb_(1-x)Fe_(x),Gd_(1-x)Fe_(x), Dy_(1-x)Fe_(x),Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co, or Dy_(1-x-y)Fe_(x)Co.
 20. Amethod for fabricating a logic cell, the method comprising: depositingand patterning a layer of conductive material on a substrate to define afirst electrode; depositing a first layer of anti-ferromagnetic materialor ferrimagnetic material directly on the first electrode; depositing adielectric material layer over the first layer; patterning the firstlayer and the dielectric material layer to define a magnetic portion anda dielectric portion of the cell; and forming a second electrode portionin contact with the dielectric material layer.
 21. The method of claim20, wherein the first layer is a first layer of ferrimagnetic materialand the method further comprises: depositing a first layer ofanti-ferromagnetic material on the first layer of anti-ferromagneticmaterial; depositing a second layer of ferrimagnetic material disposedon the first layer of anti-ferromagnetic material; depositing a secondlayer of anti-ferromagnetic material on the second layer offerrimagnetic material; and patterning the second layer of ferrimagneticmaterial and the second layer of anti-ferromagnetic material.
 22. Themethod of claim 20, wherein the ferrimagnetic material includesTb_(1-x)Fe_(x), Gd_(1-x),Fe_(x), Dy_(1-x),Fe_(x),Tb_(1-x-y)Fe_(x)Co_(y)Gd_(1-x-y)Fe_(x)Co, or Dy_(1-x-y)Fe_(x)Co.
 23. Themethod of claim 20, wherein the ferrimagnetic material includes amagnetic sublattice of rare earth ions and the sublattice formed bytransition metal ions that antiferromagnetically coupled so that momentsof the sublattices point towards opposite directions.
 24. The method ofclaim 20, wherein the conductive material includes a metallic material.25-28. (canceled)